Oil burns and smokes on grates

I've got a Weber Spirit E310 propane grill. When ever I grease the grates prior to cooking, it burns, smokes and turns the grates dark. I have tried doing this prior to heating up the grill as well as after it has heated up, but have the same results. The grates are porcelen coated cast I think. I usually preheat up to around 500 - 600 degrees for steaks, etc.

I never clean my grates. The black char gives the meat nice flavor. Once in a while i will knock of the chunks or bigger pieces but normally i leave it alone. Everyone has their own thoughts on this subject.

I have a Fire Magic E790i grill with SS grates, I clean them after every use and do a deep cleaning on the grill once every month. Your grates are, or should be porcelin coated cast.
I use EVOO and yes it can leave crud on the grill. But I usually rub whatever I'm cooking with EVOO and spices prior to putting it on.
Wit porcilin, over time little scratches develope which causes it to collect crud and food to stick.
Try using PAM for grilling it works well for me.

Is it typical that the oil on the grates smoke and turns black? I would think burnt oil would taste bad... Also, if spraying PAM, is there a problem with it going down under that grates to the flavor bars?

If you spray it heavy it'll flare up but no biggie. Since I lightly oil the food I use a very light coat on the grates, Ive never experienced a bad taste. Really, you're doing ok with it. Cleaning the grates is important though. So, no worries, experiment and have fun.

Oiling the grates and letting it burn is proven method to help foods not stick. The burning turns the oil into carbon which is black and very non stick and that is one of the reasons this method is used on cast iron pans.